The reliability of small electronic components depends to a great extent upon how well the component is hermetically sealed from reactive gases and water vapor. The test for determining the adequacy of the hermetic seal is important.
Presently, there are several methods for determining the leak rate in small electronic components. Several methods require that the electronic component be exposed to or "bombed" with a gas. Typically, the gas is helium or sometimes argon or krypton. After exposing the electronic component for a specified time and pressure to the gas, the component is removed and tested for leaks. Breaks or defects in the hermetic seal are revealed by the gas which has infiltrated the component and which is detected as a "leak" when the gas flows out of a break or defect in the hermetic seal. The tests are designed either for gross or large leaks or for fine or small leaks.
Other gross leak test methods have also been used. One such method involves exposing a small electronic component to a gas and measuring the weight gain. Another involves exposing the component to a hydrocarbon gas and measuring the hydrocarbon vapor released while pressurizing the component with another gas.
Finally, leak tests on electronic components have employed mass spectrometers. One such device is illustrated in Altshuler U.S. Pat. No. 3,578,578. Although helium leak detectors have been used for fine leak testing small electroninc components, one disadvantage is that present helium leak detectors are not totally suited for detecting large leaks in small component test objects. If a component having a large leak is subjected to a helium leak detector, all the helium may be exhausted out of the component by the vacuum system before detection measurement. In any event, such a helium leak detector reduces the apparent size of a large leak. In general, present helium leak detectors for small electronic components have inadequate sensitivity range.
Getter pumps which have been employed in ultra sensitive leak detectors (e.g., Bergquist U.S. Pat. No. 4,492,110) have not been employed in leak detectors for small components since getters are unable to quickly handle the relatively large volume of purge carrier gas which must be employed in helium leak detecting small components. U.S. Pat. No. 4,492,110 uses a nonevaporable getter pump connected to the vacuum chamber.
Cryogenic pumps have been previously employed in vacuums. One deficiency of a typical cryogenic creating pump is that it is unable to handle a relatively large volume of purge carrier gas used in leak detecting smal components. Adsorption of a large volume of gas warms up the cryogenic pump which results in desorption of the purge carrier gas. That in turn raises the pressure to an unacceptable level for the mass spectrometer. Secondly, cryogenic pumps adsorb helium and may later desorb helium which destroys the efficacy of the detection of helium by the mass spectrometer. U.S. Pat. No. 4,593,530 to Longsworth, teaches cold surfaces that freeze water and nitrogen and additionally freezes helium using charcoal as cold adsorbent.
In recently issued U.S. Pat. No. 4,608,866, Bergquist describes a leak detector where a modified cryogenic pump is connected to a vacuum chamber in such position to allow the cryogenic pump to entrap a purge carrier gas, such as nitrogen, but not entrap the detecting gas, such as helium, which is passed to a mass detector.
All of the known leak detector systems discussed above are closed systems, i.e., the test specimen or its container is subjected to a vacuum. The disadvantages of the prior systems, i.e., sensitivity and ability to detect both large and small leaks, have now been overcome by the instant open system leak detector system. While the sensitivity of the U.S. Pat. No. 4,608,866 patent is good, the present invention using an "open system" allows the rapid checking of individual small components and the rapid identification of the defective leak areas without the limitation of placing the test object under high vacuum.